Hitherto, silicone compositions which cure to give silicone rubbers are well known, and such compositions are widely used as potting materials and coating materials for electric and electronic parts and as shaping materials for moulds because of their excellent properties, such as high weather-resistance, heat-resistance, cold-resistance and electric insulating property. Additionally, techniques for imparting electroconductive properties to a silicone composition which is naturally an insulating material are also known in the art.
Imparting electroconductivity properties to a silicone composition by incorporating an electroconductive carbon black into the silicone composition is generally known. For instance, JP-A-54-139659 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses an electroconductive organopolysiloxane elastomer containing a furnace black having a specific surface area of from 40 to 100 m.sup.2 /g along with an acetylene black; JP-A-55-120656 discloses a liquid organopolysiloxane composition containing a carbon black which has a specific surface area of 900 m.sup.2 /g or more and which is partly in the form of hollow shell grains; JP-A-55-108455 discloses an extrusion-shapable liquid organopolysiloxane composition containing both a carbon black and an electroconductive fiber; and JP-A-56-120761 discloses a silicone rubber composition containing a carbon black having a specific surface area of 80 m.sup.2 /g or more.
The carbon black which is used for the purpose of imparting an electroconductivity to a resin composition as mentioned above may be classified into plural groups of a thermal black, a furnace black and an acetylene black. Above all as having a high purity, an acetylene black is used widely as a filler for imparting an electroconductivity to not only dry cells but also to other general rubbers.
In the case of a silicone rubber composition as mentioned above, however, if an excess amount of carbon black is incorporated into the composition for the purpose of imparting a high electroconductivity thereto, the excess carbon black would be incompatible with the base polymer. For instance, in the case of a millable silicone rubber composition, the plasticity of the non-vulcanized compound would thereby increase so that the fluidity of the compound during moulding would lower. As a result, severe problems would result in that the flowability into a mould, the extrudability from a mould and the roll-workability worsen extremely.
Additionally, another problem with excess carbon black-containing electroconductive silicone rubber compositions are that they do not have a highly stable and reproducible electroconductivity.
Further, another problem is that the electroconductivity of the composition often varies according to the ambient temperature so that the composition does not have a stable electroconductivity within a broad temperature range.
A silicone ink containing a curable polyorganosiloxane as a base polymer, which is diluted with a solvent, is used in various applications for coating or marking, because of the high oil-resistance and high weather-resistance of the cured silicone product. In particular, a carbon black-containing silicone ink having a high electroconductivity is used for forming contact parts of switches or for forming electric circuits.
However, a conventional carbon black-containing silicone ink which has heretofore been generally used has a drawback in that its dispersibility or solubility in solvents is extremely poor. Even after the ink has been dissolved in a solvent, it often separates easily from the solvent so that a uniform and stable ink solution is difficult to obtain.